On 2021-10-24 at 03:07:45 +1100,
Chris Angelico <ros...@gmail.com> wrote:
> def bisect(a, x, lo=0, hi=None):
> if lo < 0:
> raise ValueError('lo must be non-negative')
> if hi is None:
> hi = len(a)
>
> It's clear what value lo gets if you omit it. It's less clear what hi
> gets. And the situation only gets uglier if None is a valid argument,
> and a unique sentinel is needed; this standard idiom makes help()
> rather unhelpful:
>
> _missing = object()
> def spaminate(thing, count=_missing):
> if count is _missing: count = thing.getdefault()
>
> Proposal: Proper syntax and support for late-bound argument defaults.
>
> def spaminate(thing, count=:thing.getdefault()):
> ...
>
> def bisect(a, x, lo=0, hi=:len(a)):
> if lo < 0:
> raise ValueError('lo must be non-negative')
[...]
> The expression would be evaluated in the function's context, having
> available to it everything that the function has. Notably, this is NOT
> the same as the context of the function definition, but this is only
> rarely going to be significant (eg class methods where a bare name in
> an early-bound argument default would come from class scope, but the
> same bare name would come from local scope if late-bound).
> The purpose of this change is to have the function header define, as
> fully as possible, the function's arguments. Burying part of that
> definition inside the function is arbitrary and unnecessary.
Those two paragraphs contradict each other. If the expression is
evaluated in the function's context, then said evaluation is (by
definition?) part of the function and not part of its argumens.
As a separate matter, are following (admittedly toy) functions (a) an
infinite confusion factory, or (b) a teaching moment?
def f1(l=[]):
l.append(4)
return l
def f2(l=:[]):
l.append(4)
return l
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